Rotary dampers are known in the most varied of formations and fields of application. They are commonly provided upon automobiles in which certain parts, such as lids for glove compartments, ash trays, holding grips or like are damped in their movement. In most cases it is a case of preventing a heavy knocking of the parts against an abutment. By way of this knocking, specifically undesirable noises are produced and the lifetime of the function is compromised.
In many cases a damping is only desirable in one direction, so that the damper exhibits a free running in the opposite direction. However these are more complicated with respect to the simple rotary dampers and require more space, which commonly is not available for the installation.
A typical rotary damper comprises a housing, mostly of plastic, in which a chamber for the rotor is formed. The rotor is rotatably mounted in the housing and extends by means of shaft to one or both sides out of the housing. On one end of the shaft protruding out of a the housing, a pinion is seated which can be brought into engagement with a counter-pinion or a rack. Often the damper is stationarily applied so that an arcuate rack on the part to be damped rotates the pinion when the part is moved. In the chamber of the damper housing there is disposed a viscous medium which acts between the rotor and the chamber wall when the relative movement between the rotor and the housing takes place. For the formation of a rotor there are the most varied of embodiment forms. A typical formation consists in providing the rotor with at least one vane which radially projects into the chamber and may be observed as a type of rotating piston. With the movement of the vane in the chamber, medium is displaced which is forced through a gap between the vane and the chamber wall or which reaches the other side of the vane in another way. In this context it is also known to provide flexible vanes of a rotor for rotary dampers in order to form a differently large gap between the vane and the chamber wall, according to the rotational direction, in order to achieve an effect similar to free running in the one rotational direction.
All known rotary dampers have in common that on operation they produce a more or less constant braking moment. In some cases of application however the torque on the part to be damped is not constant but changes with the rotational position. If for example the flap of a glove compartment is opened, the flap is located approximately in the dead center position, that is exerts a very small torque in the opening direction. If the rotary damper has a relatively high braking moment the initial torque of the flap is not sufficient to set this flap in motion. If on the other hand the damper is given just a slight braking moment, then the opening speed at the end of the adjustment is too large.